The present invention relates to an acetabular cup inserting instrument which is used by a surgeon to insert and properly position an acetabular cup implant into its proper anatomical location.
A number of instruments are known in the art for inserting acetabular cup implants into position in the acetabulum. An example of one such instrument is shown in U.S. Pat. No. 4,716,894 assigned to the assignee of the present invention and incorporated herein by reference. That patent shows a cup inserting instrument with a main gripping handle and second handle which is rotatable about the first handle.
Both the main and second handles of the instrument, shown in U.S. Pat. No. 4,716,894, include grooved, radial disks that intermesh and interlock when a locking sleeve forces the two handles together. The rotatable locking sleeve locks the second handle to the main handle.
Although this instrument enables the second handle to be locked in selectable positions, when the locking sleeve is unlocked thereby disengaging the grooved disks, the second handle can fall unimpeded if it slips out of the surgeon's grasp. Therefore it is important that the surgeon maintain a good grasp on the second handle when in its released position. Free rotatability of the second handle can be prevented to a degree by backing off the locking sleeve to the point where the grooved disks are only partially disengaged. As the second handle is rotated, the teeth on the disks "jump" over each other in much the same fashion as gears that are only partially engaged. However, this jumping movement is very erratic and rough and does not provide the controlled movement that is desirable in order to accurately position the second handle when placing an acetabular cup during a hip replacement procedure.